Range and direction finding apparatus



June 13, 1950 v ROCHESTER 2,511,599

RANGE AND DIRECTION FINDING APPARATUS Filed Maxch s, 1945 N r s TRANSMITTER WA DELAY may 5 INDICATOR LINE OSClLLATOR T A L M0D ULATl/V6 MEANS I IDISC'RININATOR AHPLIFI ER usmauumrok RECEWWIG BLOCK DIAGRAM 0F RANGING DEVICE ANTENNA FHEGE GAIN g C L a aR +0 D FREQUENCY-a- PIE. 2

GAN F .1 2 FPEQUENCY 2(ZR744'D) 2D PRACTICAL FREQUENCY CHARAGTER1$TIG- Fnmfi TRANSmi-TEQ MATCHED i LOAD 7 r E I 'II I RECE\VEF? E DIREQTIOW MAYEGUIDE COUPLING TO USE 'A' SINGLE ANTENNA FOR TRANSMITTING AND RECEIVING FEE, Q INVEN TOR. M THAN/2 Qocmss 75/?- Patented June 13, 1950 ,s sss APPARATUS Nathaniel Rochester, South ton,

signor to Sylvania Electric Products Inc.,

, a corporation of cg husetts Application March a, 1945, Serial N... 580,741

This invention relates to apparatus for and method of range and direction finding.

An object of the invention is to enable the use of such apparatus by blind persons, to guide them in their motion. The visual indicating means ordinarily used in such apparatus is, of

4 Claims. (Cl. 343-) lator to modulate u. is a condition which should produce oscillation of itself, the oscillacourse, useless to such persons; but my device can produce an audible signal whose frequency the direction in which the device is oriented, and

thus the blind person may point the apparatus in a given direction, and determine how far away the nearest object in that direction is.

My device is not limited to use for such purposes, but may also beused as an altimeter for airplanes, as a range and direction finder for boats, and other vehicles, and similar uses. In the latter cases, it may be desirable to transform the audible signal into a visual indication.

A feature of the invention is an oscillating circuit including a path of wave travel, or its equivalent, which determines the frequency. The invention may embody a carrier wave whose frequeney is not changed, but which is modulated by a variable frequency; and the carrier may be any form of controllable wave, particularly radio and sound, or supersonic, waves. The invention is adaptable to amplitude, phase or frequency modulation, and will be understood from the following specification and accompanying drawings.

Figure 1 is a block diagram of this device embodying the invention;

Figure 2 is a curve of the ideal frequency characteristic of the device;

Figure 3 i s a curve of the Practical frequency characteristic; and

Figure 4 is a diagram of another embodiment of the invention using a single antenna.

In Figure 1, the carrier oscillator produces a carrier .wave which is radiated in a particular direction by the transmitting antenna. When the wave is interrupted by some proper object, which we may call the target, part of it at least, will be reflected back into the receiving antenna, from which it will be passed on the demodulator, that is to produce a wave of the modulation frequency. The latter is thus amplified and coupled back to the earner oscillator, to control the output of the latter. We thus have a circuit in which an impulse produced in the carrier oscillator is eventually fed back to the carrier oscil= tions it produces being a modulation of the carrier wave by a frequency that depends on the time required to feed back the impulse. Under these circumstances, neglecting all other delays, the modulation frequency emerging from the transmitting antenna at a particular phase must reach the receiving antenna in the same phase in order to reinforce the oscillation. In other words, the oscillation can only be sustained if its wavelengthis equal to the distance travelled by the wave between the two antennae, or is a sub multiple thereof. This distance travelled by the wave will be double the distance to the target, and the fundamental frequency will accordingly be C/2R, where C is the velocity of light and R the distance from the antennaeto the target. The antennae will ordinarily be close enough together to be considered as at the same point.

The conditions for oscillation will also be fulfilled if the frequency is an even multiple of g/gZR, that is, if it is KC/ZR, where K is an in- The foregoing assumes that there is no phase reversal and no delay in the circuit except that due to the transit of the wave from transmitter to receiver. If there is no cross-coupling directly between the two antennae, such an arrangement would be satisfactory. In most cases, it is diflicult to prevent such cross-coupling, and in some cases it may produce a greater signal than the signals returned from the target. To prevent this, a delay line, such as a filter network or the like, may be introduced between the ampliher and the carrier oscillator, as shown in Figure 1. Since the distance between the two an-' tennae is small, the frequency of the modulation oscillation due to cross-coupling will then be the frequency corresponding to the delay introduced by the delay line. The cross-coupling oscillation can then be prevented by arranging the amplifier to use a band rejection filter cutting ed at the frequency at which the delay line produces oscillations. Under the conditions previously discussed this would be C/D.

If, however, we use an amplifier in which the phase of the output difiers by from the phase of the input, because of a transformer connection or, in a direct-coupled amplifier, the use of an uneven number of tubes, the frequency will be different. The signal wave will then have to reach the receiving antenna at a period corresponding to an uneven number of half waveoran uneven number multiple thereof. Since animevennumbercanberepresentedbyia-l-h thepoaiblefrequencieswillbe a so (2a+1)C runes) 2(1 +2a 2 n+2a tion would be, if it occurred:

g E...(2n+1)c "'2D 2D 2D 'I'hebandrejectionfilterforthiscaseshould have its cutoifat C/2D, as showninrigure 2. Ofcourse,arectangularcut-ofiis impossible to achieve practically, but a cut-off such as that in the curve of Figure 3 is well-knowmas obtain-' able with equally well-known filters. The main requirement is that the filter actually rejects (2/20; the small on above this is not harmful, along as it falls oil before the next frequency 3C/2D is reached. The cross-coupling oscillation will thus be prevented. There is one further requirement of the amplifier gain characteristic of figures l and 2. The

Andthefrequencyofthecrcss-couplingoscillafrequency of the modulation oscillation will go down as the distance to the target increases. The lowest frequency will thus correspond to a target at this maximum range, Rm, desired.v This'frequency will be, for the fundamental,

The amplifier, with its filter, will have to transmit this wavelength, but will not have to transmit any lower fr encies.

The second mode of oscillation for a target at maximum range will be and, if the gain of the amplifier at this frequency is great enough, one will find it impossible to distinguish such a target from a closer target at its first mode. Of course, the signal strength will be less, and if the amplifier gain is kept low enough, such spurious results will be prevented.

The gain in the amplifier should be just enough to insure oscillation with a target at maximum range. If automatic volume control is used, its lower limit of control may be kept above the value corresponding to a signal at maximum range. In any event, the amplifier and the whole feed-back circuit has a linear response characteristic over the desired frequency range (Fig. 8). in the sense that no additional demodulator is included. v In the use of my device by the blind, the possibility of a far target appearing nearer than it really is because of reception of its second mode, may not be too important, because as the blind person gets nearer to it the spurious effect of the second mode will disappear, and in any event the first mode will always be present.

But if we desire to eliminate the second mode from a remote target we can fix the maximum range so that its second mode is at or above the acumen .well-knowntype.whichwouldchangethefie-- '15 cut oil frequency C/ZD. This will occur if we make the delay D, of the delay line, equal to the delay of the wave in travelling to a target at maximum range and back.

. 4 Bo fanwehaveseenthat-the frequency, far objects a low frequency; Ifall the frequenciesproducedinthedesiredrameofm' tanoesareintheaudiblescaleasmallpaitofthe amplifieroutputcouldbeleddirectlyintoapair of earphones, or a device such as used for emitting soundinhearingaldsiandwornbytheblindpersonusingtheapparatus. Ifthedevicewasto bensedforotherpm'posesJl -l' oftheamplifier outputcouldheledintoadiscrlminatorofsome quency variation into amplitude variation, if

.desired, for operating a direct reading instrument. This latter could be done whether or the modulation was at audio frequencies.

However, in some cases, the frequencies produced by the modulation may not be in the audible scale for the range of desired. In this case, the frequencies would have to be reduced to aifect the blind man's ears.- This could be done, for" example, by using the amplitude variation produced by the discriminator to vary the frequency of a local audio frequency oscillator in the manner customary in frequency modulation transmitters.

The radiating and receiving antennae will ordinarily be of the type producing a fairly narrow beam, as a horn or reflector-enclosed type. In Figure 4, I have shown a system in which a single antennae may be used. The antenna is of the horn type, fed by a wave-guide, which also takes light in the direction in which the position of objects is to be determined.

For convenience, in the foregoing description, I have considered the case where the carrier wave is a radio wave, preferably a micro-wave. But 'supersonicwaves could also be used, in which case the corresponding supersonic apparatus would be substituted. Delay lines and the like are well-known also for such waves, sometimes comprising a mecury filled tube or the like. In calculation of the modulation frequency, the velocity of the particular wave used should be considered.

What I claim is:

1. A range finder having a transmitter including a generator of a sustained carrier, a receiver responsive to said carrier and to modulation that may be present on said carrier as it is received after reflection from an object whose distance is to be measured, said receiver being close to said transmitter and having only a single demodulator yielding the modulation on said carrier, and a feed-back circuit between said demodulator and said transmitter-and having a linear response characteristic, said transmitter including means energized by said feed-back circuit for modulating said carrier thereby, said carrier being modulated at a natural oscillation frequency varying as an inverse function of the distance between the range finder and the object.

2. The combination of claim 1 and indicating means energized by the output of said demodu- "later and responsive to the modulation fre- REFERENCES CITED quency of the carrier wave.

a. The combination or claim 1 in which the The followme referencesare of record in the feed-back circuit includes a. delay line for supfile this intentpresisling very high modulation frequencies dug 5 UNITED STATES PATENTS to ect feed-back between said transmitter an said receiver and without a ranging reflection. 332? ggfi 4. The combination of claim 1 in which said 2134716 Gmm 1938 transmitter and said receiver are provided with 2333'688 E'EIIIII: v: 1943 highly antenna 2,403,155 Rankin July 9, 1946 NATHANIEL ROCHESTER. 24363 Wmdyard i 1947 

